<h2>DESCRIPTION</h2>

<em>r.resamp.interp</em> resamples an input raster map by interpolating between
the neighboring cells via a selectable resampling algorithm. All cells
present in the neighborhood of the input raster cell must be non-null to
generate a non-null cell in the output raster map. A choice of four
interpolation methods is available; each uses the weighted values of a different
number of adjacent cells in the input map to determine the value of each
cell in the output map as follows:
<ul>
<li>nearest neighbour (1 cell)</li>
<li>bilinear (4 cells)</li>
<li>bicubic (16 cells)</li>
<li>lanczos (25 cells)</li>
</ul>

<p>This module is intended for reinterpolation of continuous data
to a different resolution rather than for interpolation from scattered data
(use the <em>v.surf.*</em> modules for that purpose).



<h2>NOTES</h2>

<p>Resampling modules (<em>r.resample, r.resamp.stats, r.resamp.interp,
r.resamp.rst</em>) resample the map to match the current region settings.

 
<p>Note that for bilinear, bicubic and lanczos interpolation,
cells of the output raster that cannot be bounded by the appropriate number
of input cell centers are set to NULL (NULL propagation). This could occur
due to the input cells being outside the current region, being NULL or MASKed.


<p>For longitude-latitude locations, the interpolation algorithm is based on
degree fractions, not on the absolute distances between cell centers.  Any
attempt to implement the latter would violate the integrity of the
interpolation method.


<h2>EXAMPLE</h2>

Resample elevation raster map to a higher resolution (from 500m to 250m;
North Carolina sample dataset):

<div class="code"><pre>
g.region raster=elev_state_500m -p
g.region res=250 -ap
r.resamp.interp input=elev_state_500m output=elev_state_250m \
                method=bilinear
</pre></div>

<center>
<img src="r_resamp_interp_orig_500m.png" alt="Original 500m resolution elevation map"><br>
Original 500m resolution elevation map
<p>
<img src="r_resamp_interp_new_250m.png" alt="Resampled 250m resolution elevation map"><br>
Resampled (bilinear) 250m resolution elevation map
</center>

<h2>SEE ALSO</h2>

<em>
<a href="g.region.html">g.region</a>,
<a href="r.resample.html">r.resample</a>,
<a href="r.resamp.filter.html">r.resamp.filter</a>,
<a href="r.resamp.rst.html">r.resamp.rst</a>,
<a href="r.resamp.stats.html">r.resamp.stats</a>
</em>

<p>
Overview: <a href="https://grasswiki.osgeo.org/wiki/Interpolation">Interpolation and Resampling</a> in GRASS GIS

<h2>AUTHOR</h2>

Glynn Clements

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